The present invention relates to thrust reversers for turbofan engines and, in particular, to thrust reversers of the type having a cascade array affixed in the outlet opening from the engine air duct for redirecting the air flow in the duct outwardly and forwardly when the thrust reverser is deployed.
One general type of thrust reverser for the air duct of turbofan engines is based on a translating sleeve that forms a rearward, outer wall portion of the air duct. For normal rearward air flow through the air duct, the translating sleeve resides in a closed position in which its forward end engages a bulkhead that is mounted on the fan case of the engine via a V-groove/V-blade interface. For reverse air flow, the translating sleeve is moved rearwardly away from the bulkhead, leaving an outlet opening rearwardly of the bulkhead through which air is discharged from the air duct. The thrust reverser also provides for blocking of the air duct at a location rearwardly of the outlet opening.
In one form of blocking system, a number of blocking doors are pivotally mounted on the translating sleeve and coupled by linkages to the cowl of the air turbine of the engine. When the translating sleeve moves rearwardly upon deployment of the thrust reverser, the linkages pivot the blocking doors radially inwardly to positions in which they block the air duct. Another form of blocking system is a fixed inner wall member on the translating sleeve that is located and shaped to form the outer wall of the portion of the duct inwardly of the thrust reverser outlet opening when the translating sleeve is in the forward position and to block the air duct when the translating sleeve is the rearward, reverse-thrust position.
When the translating sleeve is deployed for reverse thrust of the air flow produced by the engine fan, a cascade array, a series of fixed, circumferentially extending, curved deflector blades, located in the outlet opening formed between the bulkhead and the translating sleeve redirects the air flow in the air duct so that it flows through the cascades outwardly and forwardly. Previously known cascade arrays for thrust reversers have had a circular cylindrical arrangement. Circular cylindrical cascade arrays use the available space efficiently and are conducive to structural integration with the top and bottom slide track beams of the thrust reverser. Examples of thrust reversers of the cascade array type for the air ducts of turbofan engines are described and shown in, for example, U.S. Pat. Nos. 3,500,645 and 6,000,216, and in EP 0 109 219.
An object of the present invention is to provide a thrust reverser having a cascade array that provides for more effective use of the entire length of the cascade array in redirecting the air flow, thus permitting an increase in thrust reverser efficiency for any given size of cascade array and air flow in the air duct or allowing the size and weight of the cascade array to be reduced for any given reverse thrust and air flow. In the latter case, the required travel of the translating sleeve can also be reduced, thus yielding additional savings in weight. Furthermore, shorter cascades allow for optimized aerodynamic sleeve external lines, thus reducing drag. Another object is to provide a thrust reverser in which a cascade array is structurally incorporated in a manner that is likely to permit reductions in the size and weight of some of the structural components of the thrust reverser.
The foregoing objects are attained, in accordance with the present invention, by a thrust reverser for a turbofan engine having an air duct defined radially inwardly by a cowl around a gas turbine and radially outwardly in part by a fan case of the engine. The thrust reverser includes a bulkhead that is adapted to be mounted on the fan case. A translating sleeve is supported for movement axially between a closed position adjacent the bulkhead and an open position spaced apart axially to the rear of the bulkhead so as to form an outlet opening for discharge of air from the air duct. A cascade array fixed in the outlet opening has a substantially conical portion, the forward end of which is of a diameter substantially smaller than the diameter of the rearward end.
The conical portion of the cascade array permits the forward cells of the cascade array to be located closer to the air flow in the duct than in conventional cylindrical cascade arrays, thus enabling an increased air flow through the forward cells and improving efficiency. The conical portion of the cascade array also permits the forward end to be affixed to the forward bulkhead of the thrust reverser at a location radially inwardly of the outer perimeter, thus reducing the torque load on the bulkhead and permitting it to be made smaller and lighter.
The conical portion of the cascade array does not have to be a true cone and may have a curvature in the axial direction while still preserving the advantages derived from having the forward end closer to the air flow for more effective use of the cells of the entire array, especially those near the forward end.
The cascade array may be substantially conical throughout its axial extent and arranged in line or close to in line with the outer V-groove of the fan case. Loads transferred from the cascade array to the bulkhead act generally in line with the V-groove, thus minimizing torque loads exerted by the cascade array on the bulkhead. The bulkhead can be smaller and lighter than those of previously known cascade type thrust reversers.
The cascade array of the present invention can be used with particularly important advantages in a thrust reverser in which the translating sleeve has a generally conical inner wall member forming a portion of outer wall of the duct when the translating sleeve is in the closed position and forming a blocking wall for closing the duct to rearward air flow when the translating sleeve is in the open position. The absence of pivoting doors for closing the air duct and the linkages and brackets associated with such doors allows the cascade array to be located very close to the air flow path in the duct, especially in the upstream area of the outlet opening near the bulkhead.
For a better understanding of the invention, reference may be made to the following description of exemplary embodiments of the present invention, taken in conjunction with the accompanying drawings.